A cooling device is used to cool specific space by circulating refrigerants according to a cooling cycle. The cooling device includes a refrigerator, a kimchi refrigerator, an air conditioner, etc. The cooling cycle is to change refrigerants to four stages of compression, condensation, expansion, and evaporation. In order to perform the cooling cycle, a compressor, an expansion valve, a condenser, and a heat exchanger such as an evaporator should be provided.
That is, in the cooling device, refrigerants in a gaseous state are compressed by driving the compressor, the compressed refrigerants are sent to the condenser so as to be cooled through heat exchange with ambient air in the condenser, the flow of the refrigerants changed to a liquid state by cooling is adjusted by the expansion valve and then sprayed into the evaporator, and then the sprayed refrigerants are suddenly expanded to be vaporized. At this time, the evaporator absorbs heat from ambient air to supply cool air to internal space such as a storage chamber or indoor space, thereby cooling the space. Also, the refrigerants changed to the gaseous state in the evaporator again enter the compressor to be compressed to the liquid state. In this way, the cooling cycle is repeated.
Since the surface temperature of the evaporator of absorbing heat of the internal space through the cooling cycle to cool the internal space is relatively lower than the temperature of air of the internal space, moisture from the air of the internal space with relatively high temperature and humidity are condensed on the surface of the evaporator so that frost is formed on the surface of the evaporator. The frost formed on the surface of the evaporator becomes thicker over time, and accordingly, the heat-exchange efficiency of air passing through the evaporator deteriorates to lower cooling efficiency, resulting in excessive power consumption.
If a separate heater is included in the cooling device in order to remove the formed frost, heat generated by the heater is transferred to the frost through radiation or convection, which causes low efficiency, long defrost time, a change in inside temperature of the refrigerator, etc. Recently, studies for overcoming the problem are underway.